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This article will explain in detail how to view text in Linux, Xiaobian feels quite practical, so share it with you as a reference, I hope you can gain something after reading this article.

preface

In daily development, we often need to view various texts and logs on the server. This article mainly summarizes and summarizes the commonly used text and log viewing techniques, so that everyone can collect them for subsequent viewing:

tail command View log information

Real-time monitoring logs:

tail -f filename

Real-time monitoring of 10 lines of log information:

tail -10f filename

Look at the last 100 lines of log information at the end of the log:

tail -n 100 filename

View log information after 100 lines:

tail -n +100 filename

head command View text messages

Look at the first 100 lines of text:

head -n 100 filename

View the last 100 lines or more of text

head -n -100 filename

cat command View text messages

View all text content

cat filename

View the middle of the text between certain line ranges, say viewing text between lines 100-120:

cat -n filename |tail -n +100|head -n 20

However, individuals do not like to use this command to locate the text view, because it is too troublesome to view, the article will have a more simple command operation.

tac View text messages

The cat command is a bit of the opposite of the cat command. The cat command is more about presenting the text from the head to the end, while the tac command is about presenting the log content from the end of the text to the head.

tac filename

For example, let's say we use cat and tac to view the same piece of content simultaneously:

Display the text through different commands and you will find that the order of the text content is reversed.

Search for text content

Grep is a powerful text search tool that searches text using regular expressions and prints out matching lines.

Common ways to use grep:

Find in multiple files:

grep "match_pattern" file_1 file_2 file_3 ...

Tag Match Color--color=auto Options:

grep "match_pattern" file_name --color=auto //[The color item here can be selected according to the document description: always, never, auto]

Output all lines except-v option:

grep -v "match_pattern" file_name

Use the regular expression-E option:

grep -E "[1-9]+"

Output only matched content options:

grep -o -E "[a-z]+. " line

Count the number of rows in a file or text containing matching strings-c option:

grep -c "text" file_name

Output the number of rows containing matching strings-n option:

grep "text" -n file_name

After understanding the function points that grep command can accomplish, we can use it flexibly in practical work.

Sometimes we also encounter some need to view log information for a certain period of time. At this time, you can use grep to achieve this function. For example, if you want to view log information within 2019-08-06 22:00, you can enter the following command:

grep '2019-08-06 22' filename

This allows you to quickly navigate to the information you want to see.

Since the grep command can receive standard input data, we can usually use the pipe command character "|"to perform lookup operations in some standard output in progress.

For example, first read the contents of the file, and then use the help of the pipeline to forward the contents to grep for content filtering, such as the following command:

cat log.file |grep -n '2019-08-06 22:43'

Instead of using grep, you can also use sed to achieve the desired effect.

SED is a non-interactive editor that processes files (or inputs) line by line and sends the results to the screen.

Perhaps for beginners, it is more direct to talk about concepts than to come directly to a few practical cases.

Common ways of sed command:

Print only the first line of the file

sed -n '1p' filename

View the file from line 1 to line 10

sed -n '1,10p' filename

Delete the first line of text information

sed '1d' filename

Replace certain strings in text

sed 's/what you want to replace/what is replaced/g' e.g. sed 's/1/one /g' filename Replace 1 with one

After understanding some of the basic uses of sed, we can use it many times in practical work scenarios to strengthen our understanding of sed.

For example, specify the date range by sed command, for example, view the log records between 2019-08-06 22:43-22:44:

sed -n '/2019-08-06 22:43/,/2019-08-06 22:44/p' filename

The above mentioned the use of head and tail commands together to achieve a view of a section of the log file, but such an operation is a bit troublesome, you may wish to try using the sed command to operate.

For example, look at lines 1-20 of the log:

nl log.file | sed -n '1,10p'

Use the more command to turn pages

If the log file you want to view is too large, you can use the more command to page search, for example, set each page to display 10 pieces of data information:

more -10 filename

By using the more command, you can view the data displayed on each page, and by hitting the space bar, you can jump to the next page. The window also displays the basic progress of the text currently being read.

Having said that, let's do some simulation scenarios:

View log entries for the last occurrence of keyword 'test'

grep 'test' -A 10 log.file | tail -n 11

Here you need to understand the meaning of several parameters of the grep command:

grep 'name' -A 10 Display matches and the next 10 lines

grep 'name' -B 10 Display matches and the first 10 lines

grep 'name' -C 10 Display matches and the first 10 lines

The tail -n 11 command displays the currently displayed 10 lines and the matching line

Simply count the number of rows in a log where the keyword 'test' appears

Corresponding orders:

grep 'test' ./ log.file |wc -l

Here we can first output the contents of the text to the standard output, and then pass the data information to the wc command for statistics through the pipeline.

Some common parameters of wc command

-l Number of rows matched

-w matching words

-m Number of characters matched

Linux inside for text information viewing skills is too much, far from being limited to what I mentioned in this article, so in the actual work we can also help ourselves to improve the efficiency of the skills summarized and summarized.

About "how to view text in Linux" this article is shared here, I hope the above content can be of some help to everyone, so that you can learn more knowledge, if you think the article is good, please share it to let more people see.

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